In recent years, thermal transfer systems have been developed to obtain prints from pictures which have been generated electronically from a color camera. According to one way of obtaining such prints, an electronic picture is first subjected to color separation by color filters. The respective color-separated images are then converted into electrical signals. These signals are then operated on to produce cyan, magenta and yellow electrical signals. These signals are then transmitted to a thermal printer. To obtain the print, a cyan, magenta or yellow dye-donor element is placed face-to-face with a dye-receiving element. The two are then inserted between a thermal printing head and a platen roller. A line-type thermal printing head is used to apply heat from the back of the dye-donor sheet. The thermal printing head has many heating elements and is heated up sequentially in response to the cyan, magenta and yellow signals. The process is then repeated for the other two colors. A color hard copy is thus obtained which corresponds to the original picture viewed on a screen. Further details of this process and an apparatus for carrying it out are contained in U.S. Pat. No. 4,621,271 by Brownstein entitled “Apparatus and Method for Controlling A Thermal Printer Apparatus,” issued Nov. 4, 1986, the disclosure of which is hereby incorporated by reference.
U.S. Pat. No. 4,910,087 discloses a heat-resistant slipping layer on the back surface of a thermal dye-donor element comprising a polyurethane or polyurea resin modified with polysiloxane bonds. There are a number of problems with this slipping layer including sticking between the dye layer and slipping layer when the donor is rolled up and head debris built-up upon processing. It is an object of this invention to eliminate or reduce such problems.
U.S. Pat. No. 5,627,130 discloses a heat-resistant slipping layer on the back surface of a thermal dye-donor element comprising a siloxane copolymer for a dye-donor slipping layer. U.S. Pat. No. 4,916,112 discloses a slipping layer comprising a nonhomogenous layer of a particulate ester wax.
U.S. Pat. No. 4,898,751 to Dwivedy discloses methods and compositions for inhibiting and/or preventing the adhesion of materials such as coal or coke to container walls due to weather conditions. The composition comprises a polymeric poly-α-olefin wax and a resin in a hydrocarbon solvent.
U.S. Pat. No. 5,939,207 to Fensore et al. discloses a dye-donor element including a release layer between a pigmented layer and a substrate, the release layer composed of an ethylene vinylacetate copolymer, an α-olefin maleic anhydride copolymer and a wax. EP 1205 313 A1 to Eike discloses a dye-donor element with a coloring layer on a substrate wherein the coloring layer is formed of a mixture of a copolymerization product obtainable by polymerizing an α-olefin/a maleic acid anhydride copolymer with a maleic acid anhydride monoester and an ethylene/vinyl acetate copolymer. Finally, US Patent Publ. 2002/0044192 to Hirano discloses a similar composition used as an adhesive layer disclosed between a coloring layer and a substrate of a dye-donor element, also referred to as a thermal transfer sheet.
A continuing problem with dye-donor elements in the prior art, especially when enabling faster printing, is sticking or friction between the dye-donor element and the thermal head, undesirable folds, and retransfer.
In particular, a problem arises with the use of dye-donor elements for fast thermal dye-transfer printing because a thin support is required in order to provide effective heat transfer. For example, when a thin polyester film is employed, it can soften when heated during the printing operation and then sticks to the thermal printing head, preventing donor transport. A slipping layer is typically provided to facilitate passage of the dye-donor under the thermal printing head. A deficiency in the performance of that layer causes intermittent rather than continuous transport across the thermal head. The dye transferred thus does not appear as a uniform area, but rather as a series of alternating light and dark bands (so-called “chatter marks”).
A desirable performance characteristic for a slipping layer is a smooth transfer across a wide range of printing conditions. Variable print forces along either the length or width of a print could cause image defects. Differences in print forces are specially magnified in regions of abrupt temperature change. At the transition from Dmax ((maximum print density) to Dmin (minimum print density), the force may spike upward from Dmax to a peak force and then return to Dmin. This differential is referred to as “pops” since an audible popping noise can be heard in extreme cases during printing.